This invention relates to a process for the metered introduction of fine-grain materials, particularly pulverulent solid substances (i.e., coal dust) from a pressurized metering container which contains a supply of solid material, into an industrial furnace having a plurality of feed locations such as a blast furnace or cupola furnace. The solid material is fed to the individual feed locations in a carrier gas stream through a conveying duct, the gas stream being highly charged with the solid material. The carrier gas is fed to the lower end section of the metering container in a flow which causes a local loosening in the lower section of the supply of solid material with the conveying ducts opening into the loosening region.
The present invention further relates to an apparatus for carrying out the above-mentioned process. This apparatus includes a metering container, which is designed as a pressure vessel and which is adapted to be filled at its upper end section with solid material to be fed to the furnace. The metering container includes at its lower end section a plurality of upwardly open chambers. At least one conveying duct leading to a feed location opens into each of the chambers. The conveying ducts are provided in each instance with a gas-permeable incident flow floor. Also, on the side of each conveying duct remote from the metering container a carrier gas duct for the carrier gas feed communicates therewith.
In order to conserve high-grade fuels such as, for example, oil or coke, a portion of the fuel may be replaced by coal dust. Such coal dust is typically obtained from raw coal in a pulverizing and drying plant. The coal dust is fed to an industrial furnace by means of an appropriate pneumatic conveying device.
In this connection, the most important metallurgical requirement comprises metering of the furnace dust, that is, the quantity of coal dust fed to the furnace per unit time. This metering must take place with the greatest possible accuracy so that the metallurgical processes in the furnace are subjected to the smallest possible fluctuations.
Yet another important metallurgical requirement is that since the coal dust is not supplied at one location, but is to be fed to each tuyere, industrial furnaces (i.e., blast furnaces) generally have a plurality of feed locations presenting a further requirement that the coal dust must be fed uniformly in each instance to the individual feed locations.
Different solid materials or types of solid materials generally possess different fluid-mechanical properties under the same conditions, and accordingly show different conveying behavior, which may be determined empirically. The carrier gas flow to be fed to the chambers of the metering container below the incident flow floors must (at least) be dimensioned in such a manner (in the case of the type of solid material to be conveyed), so as to give rise to an adequate loosening of the solid material in the local loosening zone (even at the highest operating pressure occurring in the metering container). In other words, the so called loosening point of the solid substance bed present in the metering container is achieved or exceeded in any operational condition. In the case of a fine-grain solid substance, this loosening point is only insignificantly dependent upon the pressure the solid substance bed is under.
In order to solve the existing complex problems, various proposals have already been made in the literature and, in some cases, have also been already tested, at least experimentally. However, it has not yet been possible for the proposed solutions, in existence to date, to optimally satisfy the requirements to be placed on such a process and a device for carrying out the process.
Thus, for example, in German Offenlegungsschrift No. 2,934,130, it has been proposed that both the regulation of the total conveying power of solid substance to be fed to the furnace (all conveying ducts), and the regulation of the solid substance conveying powers of the individual conveying ducts, should take place by variation of the quantity of carrier gas fed to the lower end section of the metering container. This takes place by means of dust flow measuring positions which are associated with each individual conveying duct. The dust flow measuring positions act in each instance on a setting valve, which is disposed in each carrier gas feed duct. However, such regulation of the conveying power by means of the carrier gas flow does not always lead to the desired results. With regard to this technology, it should be stated, inter alia, that a quantitative measurement of the solid substance component of such two-component flows is relatively inaccurate, if the intention is that absolute values should be determined by such a measurement. It should be added that, in the case of the mode of operation proposed in German Offenlegungsschrift No. 2,943,130, a precise regulation of the conveying powers of the individual conveying ducts can be achieved only with difficulty, since the variations of the carrier gas supply which are initiated by the dust flow measuring positions can greatly alter the state of fludization of the solid substance at the start of the conveying ducts.